GB2035930A

GB2035930A - Four-wheel drive transmissions

Info

Publication number: GB2035930A
Application number: GB7936037A
Authority: GB
Original assignee: Rover Co Ltd
Current assignee: Rover Co Ltd
Priority date: 1978-10-17
Filing date: 1979-10-17
Publication date: 1980-06-25

Abstract

A four wheel drive vehicle has an in-line engine (11) and a gearbox (13) including an input shaft (14), a mainshaft (15), and a two speed output drive unit (27) driven from the mainshaft. Output drive unit (27) may comprise an epicyclic gearset (30) and a differential unit (29), a clutch serving to lock the epicyclic gearset elements together to provide two output speed ranges. The overall power unit is thus simpler and more compact. <IMAGE>

Description

SPECIFICATION Improvements relating to gearboxes This invention relates to four wheel drive motor vehicles.

Until now, four wheel drive vehicles have commonly included an in-line engine coupled to a principal change-speed gearbox comprising an input shaft, a co-axial output shaft supporting a set of spur gears selectively engageable therewith, and a layshaft mounted beside and parallel to the input and output shafts. Drive is transmitted from the input shaft to the layshaft by a single set of spur gears and thence to the output shaft through spur gears fixed to the layshaft and meshing with the aforesaid gears on the output shaft.

From the principal gearbox, drive is transmitted to a transfer box comprising a spur gear driving a compound idler gear having two gear rings of different diameters. Each of the two gear rings can be mated selectively with a respective spur gear on a shaft connected to shafts transmitting drive to the front and rear axles.

The present invention provides a four wheel drive vehicle having: (a) an in-line engine; (b) a gearbox input shaft and a plurality of gears rotatable therewith; (c) a gearbox mainshaft rotatably supporting a plurality of gears that each mesh with a respective gear on said input shaft and that are selectively engageable with said mainshaft; (d) a two speed output drive unit driven from the mainshaft; and (e) front and rear wheel drive shafts driven by said output drive unit.

Thus the invention enables a simplified construction of both the principal gearbox and the transfer box.

In one form the output drive unit comprises an epicyclic gearset one element of which is connected to a coaxial gear driven by a gear on the gearbox mainshaft.

In another form the output drive unit comprises an output shaft connected to the front and rear wheel drive shafts, and a pair of gearsets each comprising a gear on the gearbox mainshaft and a gear coaxially mounted on said output shaft, clutch means being incorporated to enable drive to be transmitted selectively through either of the pair of gearsets.

Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional side view of an engine and a gearbox assembly according to a first embodiment of the invention, in combination with front and rear final drive units; and Figure 2 is a cross-sectional side view of a gearbox assembly according to a second embodiment of the invention.

Fig. 1 shows an engine unit 11 for in-line mounting in a four-wheel drive vehicle. Engine unit 11 is connected through a clutch 1 2 to a gearbox assembly 1 3 comprising a principal change-speed gearbox having an input shaft 14 carrying a plurality of spur gears which mesh with spur gears on a mainshaft 1 5. The gears on input shaft 14 are formed integrally with the shaft, while the gears with which they mesh are rotatably supported by output shaft 1 5 and can be selectively engaged therewith by dog clutches with friction synchronisers.Five ratios are available for driving a vehicle forward using gearsets 16, 17, 18, 1 9 and 20, while a single ratio is available for driving the vehicle in reverse, as provided by gearset 21 which includes an idler gear (not shown). Output from the principal change-speed gearing is by a spur gear 22 mounted at the end of mainshaft 1 5 which is nearer to engine unit 11.

Shafts 23 and 24 emerge from the gearbox in substantially opposite directions and are connected to front and rear final drive units 25 and 26 respectively, each final drive unit incorporating a differential and transmitting drive to nearside and offside road wheels of the vehicle.

An output drive unit 27 includes a gear 28 which meshes with spur gear 22 and which drives a differential unit 29 through an epicyclic gearset 30. Differential unit 29 transmits drive to the shafts 23 and 24 through universal joints 31 and 32. Epicyclic gearset 30 provides two mutually alternative ratios which are selectable independently of the principal change-speed gears, and thus provides the "high" and "low" ranges of overall gear ratios customarily available in four-wheel drive vehicles for on and off-road conditions respectively.

Epicyclic gearset 30 comprises a sun gear 33 fixed to the hub of gear 28, a planet carrier 34 formed integrally with the casing of differential unit 29, and an annulus 35. A clutch (not shown) enables annulus 35 to be locked either to the casing of the gearbox to provide the "low" ratio range, or to the planet carrier to effectively seize the epicyclic gearset to provide the "high" ratio range.

Fig. 2 shows a gearbox in accordance with an alternative embodiment of the invention in which parts corresponding to those described in relation to the Fig. 1 embodiment are denoted by identical numbers suffixed by indices.

In Fig. 2 input shaft 14' and mainshaft 15' and their associated gearsets 16', 17', 18', 19' and 20' are arranged identically to those of the previous example with the exception that the input shaft gearwheel of gearset 20' is omitted. The remaining gearwheel of gearset 20' is, as before, rotatably mounted on the mainshaft 15' and can be locked for rotation therewith by means of a dog clutch 36. Gearwheel 20' meshes with a gear 37 mounted on the elongated tubular differential casing 38.

Spur gear 22' meshes with a gear 39 which is rotatably mounted on differential casing 38, but which can be locked to the differential casing for rotation therewith by a dog clutch 40. Differential unit 29' drives output shafts 23' and 24', the shaft 23' passing through the hollow interior of the elongate tubular differential casing 38, which drive front and rear final drive units (not shown), as in the previous embodiment.

Unlike the embodiment of Fig. 1, that of Fig. 2 provides only four ratios in the principal change-speed gearing for driving a vehicle forward. The gearset comprising gears 20' and 37 is used in conjunction with the gearset comprising gears 22' and 39, in the output drive unit to provide two mutually alternative ratios selectable independently of the principal change-speed gears. Thus when dog clutch 36 is engaged, drive is transmitted from mainshaft 15' to differential unit 29' by gears 20' and 37 to give a "high" ratio range. Simiarly, engagement of dog clutch 40 causes drive to be transmitted through gears 22' and 39 to give a "low" ratio range. The operation of dog clutches 36 and 40 is interlinked such that when dog clutch 36 is disengaged, clutch 40 is engaged and vice versa.

It will be seen that in both cases the above embodiments offer simple yet effective means of providing four wheel drive. In particular, because the output from the principal changespeed gearbox is from the ainshaft, it is possible to drive the gearbox output shaft through a simple spur gear drive without the need to incorporate an additional idler gear or, as sometimes required hitherto a chain drive, to offset the front drive shaft sufficiently to clear the side of the engine. Moreover, because output from the mainshaft is at its end which is closer to the engine, the overall shape of the power unit is made more compact and its overall length reduced compared with units having a transfer box mounted on the end of the principal gearbox.

Claims

1. A four wheel drive vehicle having (a) an in-line engine (b) a gearbox input shaft and a plurality of gears rotatable therewith (c) a gearbox mainshaft rotatably supporting a plurality of gears that each mesh with a respective gear on said input shaft and that are selectively engageable with said mainshaft (d) a two speed output drive unit driven from the mainshaft and (e) front and rear wheel drive shafts driven by said output drive unit

2. A vehicle as claimed in claim 1, wherein said output drive unit includes a spur gear coaxial therewith, driven directly by a spur gear on the mainshaft.

3. A vehicle as claimed in claim 1 or 2, wherein said output drive unit comprises an epicyclic gearset, one element of which is connected to a coaxial gear driven from the gearbox mainshaft.

4. A vehicle as claimed in claim 3, wherein said output drive unit includes clutch means selectively operable to lock elements of the epicyclic gearset together for rotation in concert with one another, and to lock one element of the epicyclic gearset relative to the gearbox casing.

5. A vehicle as claimed in claim 4, wherein for a given input speed the output speed of said output drive unit is higher with all elements of the epicyclic gearset locked than it is with one element locked relative to the casing.

6. A vehicle as claimed in any one of claims 3, 4 or 5, wherein said epicyclic gearset comprises a sun gear an annulus and a carrier with planet gears, wherein input to said output drive unit is fed to the sun gear and output from the drive unit is from the carrier.

7. A vehicle as claimed in claim 1 or 2 wherein said output drive unit comprises an output shaft connected to the front and rear wheel drive shafts, a pair of gearsets each comprising a gear on the gearbox mainshaft and a gear coaxially mounted on said output shaft and clutch means to enable drive to be transmitted selectively through either pair of gearsets.

8. A vehicle as claimed in claim 7, wherein said mainshaft parallel to said output shaft and said gearsets each comprise a pair of spur gears.

9. A vehicle as claimed in claim 8 wherein said gearsets are disposed one at each end of the mainshaft.

10. A vehicle as claimed in any preceding claim, wherein said gearbox input shaft is coaxial with a crankshaft of said engine.

11. A four wheel drive vehicle substantially as hereinbefore described with reference to Fig. 1 or with reference to Fig. 2 of the accompanying drawings.